Automatic clutch apparatuses for a drive train of a vehicle, located between a drive machine and a transmission, have been known for a long time. For example, EP 0 371 975 B1 discloses a clutch apparatus, in particular, a clutch apparatus for a motor vehicle which is engaged by spring action, i.e., engaged by spring force. The clutch can be disengaged by a pressure reactive piston-cylinder combination controlled by a solenoid valve that is disengaged in this manner. Air or some other fluid medium, such as hydraulic or brake fluid, can serve as an operative means for disengaging the clutch.
It is necessary that the pressure chamber of the piston-cylinder combination be purged of air or other fluid medium so the closure spring can function properly. For this purpose, each solenoid valve or its related actuation member is regulated by an electronic control center. The maximum opening speed can be altered by the use of orifices which essentially change the effective cross-sectional flow area of the pressure lines leading to the pressure chamber. For each solenoid valve, two orifices are proposed, one for filling and one for de-aeration of the pressure chamber. These respective orifices would be opened for different durations of time as determined by a pulse modulation system. When this is done, different filling and de-aeration time ratios exist because, due to changes of the pulse modulation, the open-time for each valve is allowed to be changed.
The practice has further shown that during engagement of automatic clutches, so-called clutch engagement impacts occur (hereinafter “clutch impact” or “clutch impacts”). These sudden and forceful gear engagements detract from the driving comfort and exhibit themselves as a detectable rough step in an otherwise smooth vehicle operation and are to be avoided. Clutch impact occurs during the transition from a disengaged clutch to a partially engaged clutch during the buildup of torque. Clutch impact is noticeably apparent to and undesired by the occupant during a gear stage engagement, as well as a partial gear stage engagement. This, so to speak, is a gearing resolution tooth-to-tooth problem.
The causes for such clutch impacts are numerous and can result, for example, from the transition from a holding or a gripping contact to a sliding or a slipping contact (stick slip effect); mechanical hysteresis; the curve of the spring characteristic line of the clutch wherein a non-linear path of force is inaccurately reproduced. In the case of identical levels of disengagement force, various possibilities of force travel directions and inaccuracies in interconnection of parts are available.
Recognizing this background, the invention encompasses the purpose of providing a method for the operation of an automatic clutch apparatus by which the clutch impact can be avoided as much as possible or, at the very least, the clutch impact may be minimized so that the driving comfort is improved and the vehicle operates smoothly, e.g., detectable rough gear steps are substantially avoided.